The present invention relates to a method and apparatus for making screws having a reamer section and drill section, the screw functioning as a drill screw as well as a reamer. The screw referred to in this specification means this type of screw unless specified to the contrary.
It is known in the art to employ screws to joint a first material, such as a wooden panel, to a second material, such as a metal sheet. There are several types of screws; one typical example of which will be explained by reference to FIGS. 14 to 16.
The screw has a thread section 33, a drill section 34, and reamer edges 36 in a shank 35 interlocated between the thread section 33 and the drill section 34 or in the drill section 34. The reamer edge 36 protrudes beyond the maximum diameter of the thread section 33.
When a first material 37 is to be jointed to a second material 38, such as a structure constituted by a metal panel, holes 39 are first bored by the drill section 34 and the reamer edges 36 in the first material 37. The hole 39 is free from the thread section as best shown in FIGS. 14(b) and 15(b). If the hole is not present and the thread section is forced into the first material, the two plates will become separated because of the difference between the speed at which the drill section 34 makes a hole in the second metal material and the speed at which the thread section 33 advances in the first material 37. The reamer edges 36 are constructed so that they fracture when they come into contact with the second material 38. The thread section 33 is to be engaged in the second material 38.
In the conventional screws (A) to (C), the first step is that the reamer edges 36 are shaped by means of a pinch pointing machine or any other press. This means that the conventional process requires an increased number of steps.
As a result, the production cost is increased as compared with ordinary types of drill screws. The screw (A) illustrated in FIG. 14 has no chip-discharge groove in its shank (e), thereby causing a choking problem due to the deposit of chips from the first material 37 cut by the drilling edges. This prevents smooth boring through the first material 37.
The screws (B) and (C) in FIGS. 15 and 16 have been devised to solve the problems pointed out with respect to the screw (A). They have reamer edges 36 in the land of the drill section, but the position of the reamer edges 36 is restricted in the peripheral direction. In forming the reamer edges 36, it is difficult to locate them in the restricted area. This leads to an inefficient production of screws and an increased production cost, thereby discouraging the wide use of the screws.
There is a proposal for shaping the drill section and the reamer section at the same step of process; for example, the proposal disclosed in Japanese Patent Publication (unexamined) No. 58-152919. This is to reduce the production cost. However, the specification and drawings do not disclose a full description of the method and apparatus for making the proposed screw.
The present invention aims at solving the problems pointed out with respect to the conventional screws, and has for its object to provide a method and apparatus for making the screws efficiently and economically.
Another object of the present invention is to provide a method and apparatus for making the screws with a minimum number of steps.
Other objects and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific embodiment are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description and drawings.